Abstract
G quadruplexes (G4) are higher-order DNA and RNA secondary structures formed by G-rich sequences that are built around tetrads of hydrogen-bonded guanine bases. Potential G4 quadruplex sequences have been identified in G-rich eukaryotic non-telomeric and telomeric genomic regions. Upon function, G4 formation is known to involve in chromatin remodeling, gene regulation and has been associated with genomic instability, genetic diseases and cancer progression. The natural role and biological validation of G4 structures is starting to be explored, and is of particular interest for the therapeutic interventions for human diseases. However, the existence and physiological role of G4 DNA and G4 RNA in plants species have not been much investigated yet and therefore, is of great interest for the development of improved crop varieties for sustainable agriculture. In this context, several recent studies suggests that these highly diverse G4 structures in plants can be employed to regulate expression of genes involved in several pathophysiological conditions including stress response to biotic and abiotic stresses as well as DNA damage. In the current review, we summarize the recent findings regarding the emerging functional significance of G4 structures in plants and discuss their potential value in the development of improved crop varieties.
Highlights
Double helical B-DNA is the predominant nucleic acid structure of the genome
The result conclusively showed that G2 type G quadruplex forming sequences (GQFS) were abundant, comprising more than 90% of GQFS found in all the plant species analyzed, while G3 type GQFS were found less frequently, comprising 5% of the total GQFS in each of the plant species (Garg et al, 2016)
G DNAs are considered a molecular switch for gene expression in metazoan cells (Eddy and Maizels, 2006), it is imperative to study the positional relationship of GQFS in plant genomes (Figure 2)
Summary
Double helical B-DNA is the predominant nucleic acid structure of the genome. In addition, DNA may adopt various extrahelical, non B-DNA secondary confirmations depending on the nucleotide content. It is evident that GQFS are abundant in, but not limited to, promoters (Evans et al, 1984; Kilpatrick et al, 1986), telomeres (Blackburn, 1994), ribosomal DNA (Sun et al., 1998), untranslated region (UTR) of mRNA, micro- and minisatellite repeats (Nakagama et al, 2006), and immunoglobulin heavy chain switch regions (Yu et al, 2003) Formation of these secondary structures has been associated with genomic instability and cancer progression. Genome wide distribution of G quadruplexes and their association with different genomic features led to the identification of putative G4 forming sequences within gene body or promoter region of orthologs genes in monocot and dicot plant species (Garg et al, 2016). The evolutionary conservation of GQFSs among plant species and their association with specific genomic features as described below suggest that G4 DNAs are integral parts of plant biology and are under evolutionary constraints
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